Use of a four-dimensional description of an aircraft trajectory, involving three Cartesian coordinates (x, y, z) and elapsed time t, was proposed in 1972 by H. Erzberger and T. Pecsvaradi (“4D Guidance System Design With Application To STOL Air Traffic Control”, 13th Joint Automatic Control Confer., Stanford, Calif. Aug. 16-18, 1972, pp. 445-442) and has been considered by many other workers since then. One potential problem with use of (flight) time as a fourth coordinate is that an along-track error couples into aircraft altitude. In this approach, when an elapsed time specified by flight plan coordinates is reached or exceeded, an aircraft may be required to land many miles short of, or many miles beyond, its destination. Alternatively, failure of an air traffic management (ATM) ground computer could abruptly deposit responsibility for safe separation of aircraft proceeding along the same general route onto human air traffic controllers (ATCs). One ultimate goal of an automated ATM system is to remove, or minimize reliance on, ATCs from active participation in maintenance of separation between aircraft.
What is needed is a method and system for specification of an aircraft trajectory in terms of coordinates that (1) allow use of higher capacity of traffic in a given volume of airspace, (2) define bounds on allowable along-track, cross-track and vertical errors, and (3) compensate for deviations from a time schedule so that an aircraft is not required to fly with unrealistic velocity or unrealistic angle parameters and is not required to execute a landing procedure at a location that is spaced far apart from a destination location. The approach should allow for in-flight changes in flight parameters to take account of a changed environment.